Bacteria Thrive in Hostile Human Bellies

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The harsh acidic environment of your stomach is home to many more bacteria types than previously thought, a new study indicates.

One newly identified creature in your belly is related to a species that's considered one of the hardiest organisms on the planet, a bacterium that eats radioactive wastes for lunch.

The human stomach is a pear-shaped chamber filled with a highly noxious cocktail of hydrochloric acid and protein-cleaving digestive enzymes called peptidases. This gastric soup can have a pH of 1 to 3; the pH scale goes from 1 to 14 with a lower number indicating more acidity.

The stomach protects itself from its own corrosive juices by coating its interior with a thick, continually secreted layer of mucous.

New gastric view

The medical community long believed that pretty much nothing from the outside could survive in the stomach's harsh environment. That view began to change in 1982, when two Australian scientists, Robin Warren and Barry Marshall, found spiral-shaped bacteria called Helicobacter pylori in human stomachs.

The two researchers hypothesized that h. pylori was responsible for stomach inflammation, also called gastritis, and ulcers. Doctors traditionally thought these ailments were caused by stress or spicy foods.

Later experiments—including one where Marshal actually gave himself gastritis by drinking an h. pylori broth—confirmed their suspicions, and both Warren and Marshall were awarded the 2005 Nobel Prize in Medicine for their discovery.

Since then, however, only a few other bacteria types have ever been found in the stomach.

In the new study, researchers extracted snippets of genetic material from the stomachs of 19 people and found the biological blueprints of 128 bacteria types. Many of them had never been observed in the stomach before and 10 percent were previously unknown to science.

Conan the bacterium

One of the newly discovered bacteria types is a relative of Deinococcus radiodurans, one of the hardiest organisms alive.

D. radiodurans is a so-called extremophile because it thrives in extreme environments that would kill most organisms, such as radioactive waste dumps and hot springs. While a radiation dose of 10 grays (Gy) would kill a human, D. radiodurans can take up to 5,000 Gy with no visible effect. It can survive heat, cold, vacuum, and acid. It is so resilient scientists nicknamed it "Conan the Bacterium," after the fictional barbarian warrior.

It's unclear, however, whether the new D. radiodurans relative is likewise resistant to radiation, said David Relman, a microbiologist and immunologist at Stanford University and principal investigator in the study.

"This thing could be a totally different and novel bacteria, but only because its closest relative is famous for being incredibly radioresistant would we even think this one might be as well," Relman told LiveScience.

Relman said the next step is to observe the stomachs of volunteers over time to determine whether the newly identified stomach bacteria actually live there or whether they're just passing through.

"It could be possible that we have a continuous flow of organisms through the stomach and that very few of these are staying put," Relman said.

The study, lead by Elisabeth Bik of Stanford University, was detailed in a January online version of the journal for the Proceedings of the National Academy of Sciences.